The present invention pertains to a rudder propeller for boats or floating bodies, especially for inland navigation vessels with an associated nozzle as a casing to form a hydrodynamic drive rotatable around a vertical axis, as well as a control device, wherein the rudder propeller is arranged on the hull beneath the boat bottom or in a propeller tunnel, and the drive power is transmitted through an essentially vertically arranged stem by means of a shaft to a bevel gear which is located in a hub pivotable with the stem around the vertical axis, and drives an approximately horizontal propeller shaft. Such rudder propellers, which are also designated as so-called azimuthal propellers, are known in the art. The propeller is arranged pivotably around a vertical axis for changing or maintaining course, as well as for stopping and reversing direction of travel.
In boats intended for limited depths of water, the boat bottom is made higher in the range of the propeller than the part of the boat bottom located at the level of the baseline, so that the lower wing tip of the propeller is only slightly below the baseline if at all.
Protection of the propeller from touching the ground is absolutely necessary for inland navigation vessels. To achieve this, the boat bottom in the range of the propeller is often designed in the form of a tunnel, whose greatest curvature, being the apex, is often so high above the water line that the propeller does not cut below the baseline of the boat bottom.
In the case of draft limitation, one basic problem of the arrangement of the drive is that only propellers whose diameter is smaller than the optimal diameter for efficiency can be accommodated in the space of limited height between the baseline and the greatest possible tunnel height determined according to hydrodynamic and practical criteria in the particular case. Since, propeller efficiency increases with increasing diameter and decreases with rising thrust coefficient in the load range involved, it is necessary to accommodate the largest possible propeller diameter, especially in the case of high-load propellers. This also applies to the case in which the propellers have an annular casing with an airplane wing-like nozzle profile, which is known, e.g., as a Kort nozzle, to improve efficiency.
Prior-art arrangements of rudder propellers with nozzles have the shortcoming that the nozzle ring fastened to the stem of the propeller rotates with the propeller around the azimuthal axis and the nozzle ring is at the same time designed as a full ring within the tunnel height. As a result, the apex of the tunnel is not touched by the inner circle of the nozzle, but the inner circle lies markedly lower. At equal tunnel height, the internal diameter of the nozzle ring and consequently also the diameter of the propeller are therefore substantially reduced, and the efficiency of the propeller is therefore relatively low.
In contrast, the upper sector of the nozzle ring, which is designed completely annulary, offers hardly any advantage, because circulation around the nozzle profile and consequently the effect of the nozzle are highly insufficient there due to the components of the vertical stem and the proximity of the tunnel wall.
Due to these disadvantages and the resulting reduction of efficiency, the use of a rudder propeller with a nozzle, which is advantageous because of its special maneuverability and for other reasons, is highly limited, especially in heavily loaded tunnel boats, and is used relatively rarely, for example, in push boats, in which the elimination of very extensive stearing gears would be highly advantageous.